Oxidation process

ABSTRACT

A hydrocarbon conversion catalyst containing a Group VIB metal on a porous refractory oxide is prepared by impregnating support particles with a solution containing Group VIB metal components and citric acid, followed by drying and calcining. The catalyst is useful for promoting a number of hydrocarbon conversion reactions, particularly those involving hydrogenative desulfurization, demetallization and denitrogenation.

RELATED APPLICATIONS

This application is a divisional application of application U.S. Ser.No. 595,260, filed Mar. 30, 1984 now U.S. Pat. No. 4,568,450 which is adivisional application of application U.S. Ser. No. 409,583, filed onAug. 19, 1982, now U.S. Pat. No. 4,455,390.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to hydrocarbon conversion catalysts, such asthose utilized to catalyze the reaction of hydrogen with organo-nitro,organo-metallic and particularly organo-sulfur compounds. Moreparticularly this invention is directed to a catalyst useful for thehydrodesulfurization of hydrocarbons, such as gas oils and residuum, andto a method for preparing such catalysts by employing a novel aqueousimpregnating solution. The invention is especially directed to catalystsof high overall desulfurization activity and stability.

2. Description of the Prior Art

In the refining of hydrocarbons, it is often necessary to convert ahydrocarbon fraction to different forms. Typically particulate catalystsare utilized to promote desulfurization, denitrogenation ordemetallization reactions when feedstocks such as gas oils or residuumare contacted with catalysts under conditions of elevated temperatureand pressure and in the presence of hydrogen so that the sulfurcomponents are converted to hydrogen sulfide, the nitrogen components toammonia and the metals are deposited on the catalyst.

Conversions of hydrocarbons are often carried out with a catalystcontaining Group VIB and Group VIII metals and phosphorous on arefractory oxide support. Compositions containing these and otherelements have been previously investigated. For example, catalystscomprising a Group VIB metal, particularly molybdenum or tungsten, aGroup VIII metal, particularly cobalt or nickel, and phosphorous on analumina base have been disclosed in U.S. Pat. Nos. 3,755,196 and3,840,472. Such catalysts are very often prepared by impregnation, thatis, the deposition of the active components on the support base bycontact thereof with an aqueous solution containing the activecomponents in dissolved form. U.S. Pat. No. 3,755,196, for example,describes impregnating media and methods for preparing catalysts usingstabilized impregnating solutions consisting of molybdenum plus nickelor cobalt salts with phosphoric acid dissolved in an aqueous medium.U.S. Pat. No. 3,840,472 discloses another process for preparing a stableimpregnating solution that includes dissolving a nickel or cobaltcompound with an acid of phosphorous followed by subsequent dissolutionof molybdenum oxide. The presence of phosphorus in many conventionalcatalysts is apparently due to the method of catalyst preparation ratherthan just for catalytic activity and stability.

Although conventional catalysts, including those requiring phosphorousin their preparation, are active and stable for hydrocarbon conversionreactions, catalysts of yet higher activities and stabilities are stillbeing sought, irrespective of phosphorous requirements. Increasing theactivity of a catalyst increases the rate at which a chemical reactionproceeds under given conditions, and increasing the stability of acatalyst increases its resistance to deactivation, that is, the usefullife of the catalyst is extended. In general, as the activity of acatalyst is increased, the conditions required to produce a given endproduct, such as a hydrocarbon of given sulfur, nitrogen, and/orcontaminant metals content, become more mild. Milder conditions requireless energy to achieve the desired product, and catalyst life isextended due to such factors as lower coke formation or the depositionof less metals.

It is generally accepted that greater active component uniformity in thecatalytic particles improves activity. The formation of a more evenlydistributed layer of the active components, such as the metals and theiroxides, or sulfides, in sufficient concentration throughout the surfacearea of the catalytic support provides more efficient utilization of thecatalytic contacting surface.

Accordingly, it is an object of this invention to provide hydrocarbonconversion catalysts having a relatively evenly distributed layer ofactive components and to provide a method for using such catalysts forthe desulfurization, denitrogenation, and/or demetallization ofhydrocarbons. Another object is to provide hydrocarbon conversioncatalysts of improved desulfurization activity and stability incomparison to conventional catalysts. Yet another object is to provide acatalyst of improved demetallization and denitrogenation activity.

It is further object of the invention to provide a method preparing ahydrocarbon conversion catalyst. It is a further object still to providea method for preparing hydrocarbon conversion catalysts of improveddesulfurization activity and stability in comparison to conventionalcatalysts. Another object is to provide a method for preparing acatalyst of improved demetallization and/or denitrogenation activity.Yet another object is to provide an impregnating solution having longterm stability that may be utilized for preparing hydrocarbon conversioncatalysts. These and other objects and advantages of the invention willbe apparent from the following description.

SUMMARY OF THE INVENTION

Briefly, the invention provides for a hydrocarbon conversion catalystand for a method for preparing such a catalyst employing a novelimpregnating solution. In one embodiment, the an aqueous impregnatingsolution is prepared having a pH less than about 1.2 and containingdissolved Group VIB metal and citric acid. A catalyst compositioncomprising a Group VIB metal component on a refractory oxide is preparedby impregnating support particles with this solution, followed bycalcination. In another embodiment, a hydrocarbon conversion catalyst isprepared by the method of impregnating alumina-containing supportparticles with a stable aqueous impregnating solution having a pH lessthan about 1 and comprising dissolved ammonium heptamolybdate, nickel orcobalt nitrate and citric acid, followed by calcination. In thisembodiment the solution contains molybdenum components in a totalconcentration greater than about 10 weight percent and citric acidcomponents in a mole ratio to the molybdenum components of greater than1 to 1.

Catalysts prepared in accordance with the invention are useful forpromoting the conversion of hydrocarbons, particularlyhydrodesulfurization. A catalyst prepared with an impregnating exhibitshigh activity and improved stability when utilized to promote highconversions of organo-sulfur compounds, particularly those found inhydrocarbon gas oils, to hydrogen sulfide. Another catalyst preparedwith an impregnating solution of the invention is especially suited forpromoting the conversion of organo-metallic compounds found inhydrocarbon residuum fractions to deposable metals.

DETAILED DESCRIPTION OF THE INVENTION

Hydrocarbon conversion catalysts of the present invention are preparedwith impregnating solutions containing citric acid and having relativelylow pH values. The solutions contain dissolved citric acid and Group VIBmetal components, with the preferred Group VIB metals being molybdenumand tungsten, with molybdenum being most preferred. The solutions mayalso contain Group VIII metal components, especially cobalt or nickel,usually in a total concentration from about 1 to about 10 weightpercent, calculated as the monoxide. The mole ratio of the citric acid(as the monohydrate) to the Group VIB metal components (as the trioxide)in the solution is usually greater than about 1 to 1 and preferably atleast about 1.5 to 1. Preferably, the solution contains one or moreGroup VIB metal components in a total concentration of at least 3 weightpercent, calculated as the metal trioxides, and more preferably in therange from about 5 to about 50 weight percent.

The impregnating solution of the invention may be most convenientlyprepared by dissolving into water a Group VIB metal compound and citricacid such that the resulting solution has a pH preferably less thanabout 1.2, more preferably less than about 1.0, and most preferably fromabout 0 to about 1.0. Generally, either the citric acid or Group VIBmetal compound is first dissolved in the aqueous medium under conditionswhich will effect dissolution and provide the specified concentrationsof components. At atmospheric pressure, any temperature in the range ofabout 35° F. to about 210° F. may be employed, but it is generallypreferred to use a temperature of about 75° F. to about 150° F. It ispreferred that the citric acid be added to the solution afterdissolution of at least a portion of the Group VIB metal component,especially when an impregnating solution is desired that contains arelatively large proportion of Group VIB metal components, typically ina total concentration greater than about 10 weight percent. In additionto lowering the pH of an aqueous solution, the presence of citric acidin the impregnating solution reduces the length of time required todissolve a given amount of Group VIB metal component and, moreimportantly, increases the total amount of Group VIB metal componentswhich can be dissolved therein. For example, under the same temperatureand pressure conditions effecting dissolution, an impregnating solutioncontaining a maximum total concentration of about 10 weight percent ofGroup VIB metal components and no citric acid requires more time todissolve and is less stable than a solution containing citric acid andhaving a maximum total concentration from about 10 to about 30 weightpercent of Group VIB metal components.

Citric acid is conveniently used to increase the stability of theimpregnating solution, typically when added in such an amount that themole ratio to the Group VIB metal component is greater than about 1to 1. Stability of the impregnating solution is generally increased asthe mole ratio is increased; however, extremely high mole ratios, suchas those greater than about 10 to 1 may have economic limitations andare usually avoided. A stable impregnating solution of the invention isessentially free of precipitating components and the dissolvedcomponents remain in solution for a time period sufficient to impregnatecatalyst support particles without the formation of crystallinedeposits. Furthermore, the stable impregnating solutions of theinvention may be stored for a long term, such as a day to a week ormore, prior to effective impregnation of support particles.

Citric acid may be added to the solution in liquid or solid form. Apreferred compound is citric acid monhydrate, although any suitable formof citric acid or its precursor may be utilized.

A variety of Group VIB metal components may be utilized to produce astable impregnating solution of the invention. In general, all Group VIBmetal compounds soluble in aqueous media, particularly those ofmolybdenum or tungsten, may be utilized. The oxides of molybdenum (e.g.,molybdenum trioxide) are useful, as are many salts containingmolybdenum. Particularly useful are salts containing both a Group VIBmetal and ammonium ion, such as ammonium dimolybdate, and mostpreferably ammonium heptamolybdate. Impregnating solutions containingammonium ions are highly preferred, especially when the ammonium ion ispresent in a concentration exceeding 1.5 moles per liter, and preferablyexceeding 1.9 moles per liter.

After dissolution of the Group VIB metal and citric acid, a Group VIIImetal component may then be added to the impregnating solution. SuitableGroup VIII metal compounds are water soluble, and usually include anoxide, carbonate, and preferably a nitrate of cobalt, nickel, andchromium, or combinations thereof. The nitrate of cobalt and nickel arepreferred, with cobalt nitrate most preferred. Preferably, the finalsolution contains Group VIII components (as the monoxide) in a totalconcentration between about 1 and 10 weight percent and more preferablyless than 6 weight percent.

After addition of a Group VIII compound, the pH of the solution may dropbelow about 1.0, but if the solution remains above about 1.2, more acidis added to lower the pH preferably below about 1.2, and more preferablybelow about 1.0, and most preferably below about 0.8. The ac:dr used tolower the pH may be any acid containing thermally decomposable anions oranions not resulting in undesirable compounds in the final catalyst.Citric acid is, of course, preferred, but others such as dilute nitricacid, dilute sulfuric acid, dilute hydrochloric acid, depending upon thefinal catalyst composition desired, may be suitable to lower the pH. Anacid of phosphorus, such as orthophosphoric acid (H₃ PO₄) or aphosphoric acid precursor, may conveniently be utilized when phosphorusis an additionally desired component of the final catalyst composition.

One unusual feature of the invention is that the impregnating solutionis stable even when containing a relatively large proportion of GroupVIB metal components, i.e., in a total concentration greater than about10 weight percent. When the pH of the impregnating solution is belowabout 1.2, essentially no crystalline deposits or crystallineaggregations are detected in the impregnating solution that result in alessening in hydrocarbon conversion activity in the final catalyst.

Several conventional methods may be employed to impregnate the catalyticsupport particles with the solution of this invention. One such method,commonly referred to as the spray impregnation technique, involvesspraying the support with the impregnating solution. Anotherimpregnating method, often used to maintain relatively lowconcentrations of active components in the solution, is the circulationor multi-dip procedure wherein the active support is repeatedlycontacted with the impregnating solution with or without intermittentdrying. However, in order to take advantage of the stability of thesolution of the invention and especially when relatively highconcentrations of Group VIB metals are desired, the pore volume or poresaturation technique is preferred. This method involves dipping thecatalyst support into an impregnating solution having a volume usuallysufficient to just fill the pores of the support and, on occasion, maybe up to about 10 percent excess. The concentrations of activecomponents in the solution during impregnation by this technique may besomewhat higher than those utilized in other methods because the ratiosof active components in the final catalyst are determined directly bysolution composition.

The impregnating solution of the invention may be utilized toincorporate metal components with any of a number of support particles.Support particles suitable for use herein include such refractory oxidesas silica, magnesia, silica-magnesia zirconia, silica-zirconia, etc.Other suitable supports include natural and synthetic crystalline andamorphous aluminosilicates and crystalline silicas, e.g., silicalite.Preferred refractory oxides comprise aluminum and are usually selectedfrom the group consisting of alumina and silica-alumina. Gamma aluminais the most highly preferred support.

The foregoing refractory oxides are usually prepared in the form ofshaped particulates by methods well-known in the art, with the preferredmethod being to extrude an inorganic refractory oxide gel, such aspeptized alumina gel, through a die having openings therein of thedesired size and shape, after which the extruded matter is cut intoextrudates of desired length. Preferred refractory oxide particles areof cylindrical shape having a cross-sectional diameter of 1/32 to 1/8inch and a length of 1/32 to 3/4 inch. Also preferred are refractoryoxide particles having lengths between 1/32 and 1/8 inch and havingcross-sectional shapes resembling that of a three-leaf clover, as shown,for example, in FIGS. 8 and 8A of U.S. Pat. No. 4,028,227. Otherpreferred particulates are those having quadralobal cross-sectionalshapes.

Refractory oxide support particles prepared in the form gel extrudatesare generally pre-calcined prior to impregnation, especially if gammaalumina is the desired support material. Temperatures above about 900°F. are required to convert the alumina gel to gamma alumina. Usually,temperatures above about 1,100° F. are utilized to effect thistransformation, with holding periods of one-half to three hoursgenerally being utilized to produce preferred gamma alumina extrudates.

The amounts of active components retained on the support particlesduring impregnation will depend largely on physical characteristics ofthe support particles, inter alia, surface area, pore volume and poresize distribution. Broadly speaking, the support particles have asurface area of about 10 to about 400 m² /gram (as measured by theB.E.T. method), a pore volume from about 0.15 to about 1.5 cc/gram (asmeasured by standard mercury and helium differential density tests), andessentially any pore size distribution over a range of pore diameters assmall as about 25 angstroms to as large as about 10,000 angstroms.Selection of a particular pore size distribution of the supportparticles depends in large part on the particular hydrocarbon conversionreaction that is to be promoted by the final catalyst. For example, ifdemetallization of a residuum oil is desired, the support particles areselected with a pore size distribution such that the final catalyst hasat least about 5 percent of the pore volume in pores having a diametergreater than 100 angstroms and preferably an average pore diameter fromabout 125 to about 250 angstroms. On the other hand, a pore sizedistribution of support particles utilized to produce a final catalysteffective for desulfurization of gas oils should include pores sizessuch that the final catalyst has at least about 50 percent of the porevolume in pores having a diameter from about 70 to about 130 angstroms.

In addition to such physical properties, the surfaces of the supportparticles utilized in a final catalyst also exhibit chemicalcharacteristics that are, in part, related to a particular hydrocarbonconversion reaction to be promoted. One chemical characteristic of thesurface of the support particle is the pH value of 50 milliliters ofdeionized water containing 10 grams of the support particles standingfor 30 minutes at ordinary temperatures Hereinafter, such a measurementtechnique shall be referred to as the "support pH test." Typically,support particles utilized in the preparation of catalysts of thisinvention yield a pH value, according to the support pH test, of about 5to about 9, preferably about 5 to about 7.5 when hydrocarbondesulfurization or denitrogenation is a desired conversion reaction, andpreferably about 6.5 to about 9 when demetallization is a preferredreaction. Furthermore, support particles yielding a pH value from about6 to about 8, and more preferably 6.5 to about 7.5 usually are dualfunction, having suitable activities for both desulfurization anddemetallization.

In one embodiment, the support particles are "prewetted" prior toimpregnation. The support particles may be "prewet" by contact withwater after pre-calcination such that at least 10 percent of the porevolume, and most preferably at least 30 percent, but not more than 50percent of the pore volume, is filled with water. When the pores of thesupport particles are thus partially filled with water by this "pre-wet"method, the resulting catalyst, especially one containing less thanabout 10 weight percent of Group VIB metal components, will usually befound to have greater activity and stability for promoting hydrocarbonconversion reactions than if prepared without "pre-wetting."

Control of the contact time (aging) of the support particles with theimpregnating solution improves homogeneity of the active components onthe support. It is preferred to age the impregnated particles in theimpregnation solution for at least about twenty minutes but usually lessthan about two hours before drying and calcining. However, the particlesmay be aged for up to eight hours or longer, especially when solutionscontain a relatively high concentration of Group VIB metal components,typically, greater than 10 weight percent. Substantially evendistribution of active components in the support results from aging thesupport particles under mild conditions, i.e., 50° F. to about 100° F.,while utilizing the pore saturation method of impregnation.

After impregnation, the support is dried and calcined to produce acatalyst containing the active components in desired proportions. Theimpregnated support particles may be dried and then calcined at atemperature of at least 750° F., and preferably from about 800° F. toabout 1,200° F., so as to convert the active metals to their oxideforms. However, impregnated support particles containing a significantportion of nickel are calcined at a temperature preferably less thanabout 1,000° F., although support particles containing significantcobalt amounts may preferably be calcined up to about 1,200° F.Furthermore, when calcining support particles impregnated with asolution of the invention containing a Group VIII metallic nitrate,flowing air is usually passed at a sufficient rate over the supportparticles to remove both the nitrogen oxide (NO and NO₂) and carbondioxide (CO₂) produced by the exothermic reactions associated withnitrate and citric acid component decomposition.

Calcination of the impregnated support particles results in asubstantial portion of the citric acid being removed. However traceamounts of carbon may remain after calcination and generally the finalcomposition contains less than 0.5, preferably less than 0.1, and mostpreferably 0 weight percent carbon, calculated as C.

The final composition of the catalyst of the invention contains a GroupVIB metal component and, optionally, a Group VIII metal component on arefractory oxide. The final composition generally contains at leastabout 3 and preferably between about 5 and about 50 weight percent GroupVIB metal components, calculated as the trioxides, and, if present, fromabout 0.5 to about 10 weight percent Group VIII metal components,calculated as the monoxide. It is more preferred when the catalyst isutilized to promote a desulfurization reaction during the processing ofa hydrocarbon gas oil that the final composition contain greater than 10weight percent, and most preferably between about 17 and about 30 weightpercent of Group VIB metal components and preferably less than about 6weight percent, and most preferably between about 1 and 4 weight percentGroup VIII metal components. In another preferred embodiment in whichthe catalyst is utilized to promote demetallization reactions in aresiduum feedstock, the final composition contains about 3 to about 17weight percent of molybdenum components, calculated as MoO₃, and from 0to about 3 weight percent of cobalt or nickel components, calculated asthe monoxide. In still another preferred embodiment, the finalcomposition contains about 17 to about 30 weight percent of molybdenumcomponents, calculated as MoO₃, and about 1 to about 6 weight percent ofcobalt or nickel components, calculated as the monoxide. The finalcomposition of the catalyst may optionally contain at least one weightpercent phosphorus, calculated as phosphorus.

Although many conventional catalysts and/or their preparations requiresome form of phosphorus, the presence of phosphorus in the impregnatingsolution or final catalyst of this invention is optional. Asdemonstrated in the examples hereafter, a catalyst prepared with thesolution of the invention, without phosphorus, is more active and stablewhen utilized to promote desulfurization reactions in hydrocarbon oilsthan are catalysts containing phosphorus. However, phosphorus may beincorporated into the impregnating solution and final catalystcomposition so as to improve the activity and/or stability of thecatalyst of the invention for promoting a different hydrocarbonconversion reaction, such as denitrogenation.

Another unusual feature of the invention is that, after calcination ofthe impregnated support particles, no crystalline deposits orcrystalline aggregations resulting in a lessening in activity orstability of the final catalyst are detected. As illustrated by exampleshereinafter set forth, a catalyst prepared with the impregnatingsolution of the invention is highly stable and active for promotinghydrocarbon conversion reactions. Better dispersed forms of activecomponents from the impregnating solution onto the support particles arebelieved responsible at least in part for the improved activity andstability of the catalysts of the invention as compared to conventionalcatalysts. Impregnation of support particles with the solution of theinvention reduces the segregation of catalytic components into inactivecrystalline species on the support.

The physical characteristics of the final catalyst composition willusually vary from those of the support particles by less than about 25percent. A catalyst composition, preferably used in the processing of ahydrocarbon residuum fraction and containing about 3 to about 17 weightpercent of Group VIB metal components and from 0 to about 3 weightpercent of Group VIII metal components, has a surface area of about 25to about 250 m² /gram, a pore volume of about 0.4 to about 1.5 cc/gram,and a pore size distribution including at least 5 percent of the totalpore volume in pores of diameter greater than 100 angstroms. In anotherpreferred embodiment, a catalyst composition used in the processing ofhydrocarbon gas oils and comprising about 17 to about 30 weight percentof Group VIB metal components and from about 1 to about 6 weight percentof Group VIII metal components, has a surface area of about 100 to about400 m² /gram, a pore volume of about 0.15 to about 1.2 cc/gram, and apore size distribution including at least 50 percent of the total porevolume in pores of diameter between about 70 and about 130 angstroms.

After calcination, the oxided catalyst is generally presulfided so as toconvert the active metal components to the corresponding sulfides.Usually the catalysts are presulfided prior to use by contact with astream of sulfiding gas, such as hydrogen sulfide-hydrogen mixturescontaining about 1 to 10 volume percent of hydrogen sulfide, attemperatures between about 200° and 1,200° F. Although presulfiding ofthe catalyst is preferred, it is not essential, as the catalyst may besulfided in a short time by contact with a sulfur-containing feedstockprocessed under hydrocarbon conversion conditions.

The catalyst of this invention may be employed in any of severalhydrocarbon conversion processes wherein catalytic composites containingGroup VIB metals or Group VIB and Group VIII metals are known to becatalytically effective, such as hydrogenation, dehydrogenation,desulfurization, hydrodesulfurization, oxidation, denitrogenation,demetallization, isomerization, cracking, hydrocracking, reforming, andthe like. The catalyst of the invention may be used to refine any of agreat number of hydrocarbon oils, such as crude petroleum oils, crudesynthetic oils such as shale oils, and fractions thereof. Preferably,however, the hydrocarbon oil will boil primarily above about 100°, andmore preferably from about 100° F. to about 1,300° F., with the mostpreferred hydrocarbon oils being gas oils boiling in the range of about600° to 1,100° F. and vacuum and atmospheric residua fractions boilingabove about 1,000° F. Other hydrocarbon oils include lubricating oils,waxes, kerosene, solvent naphthas, fuel oils, diesel fuels, jet fuels,heavy naphthas, light naphthas, cycle oils from cracking operations,coker distillates, cracked gasoline, decant oils, and the like.

The catalyst of the invention is particularly effective fordesulfurization, denitrogenation and demetallization reactions,especially when utilized to process hydrocarbon oils such as gas oilsand residuum fractions. The gas oils typically contain sulfur in theform of organo sulfur compounds, for example, mercaptans, disulfides,and the like, and are usually present in a total concentration greaterthan 5 ppmw, but more often in excess of 100 ppmw, and often in aconcentration greater than 0.1 weight percent, calculated as sulfur. Theresiduum fractions usually contain at least 1.0 weight percent ofsulfur, and metallic contaminants, usually in the form of complex metalporphyrins containing nickel and vanadium, present in a totalconcentration of at least 30 ppmw, calculated as the metals. Thefeedstocks often contain undesirable proportions of nitrogen, usually ina concentration greater than 0.1 weight percent, and typically in therange between about 0.2 and 0.4 weight percent.

A hydrocarbon conversion catalyst of desired chemical and physicalcharacteristics, as prepared in accordance with the invention, isusually employed as either a fixed or fluidized bed of particulates in asuitable reactor vessel wherein the hydrocarbon oil to be treated isintroduced and subjected to elevated conditions of pressure andtemperature, and a substantial hydrogen partial pressure, so as toeffect the desired degree of conversion of, for example, sulfur,nitrogen and metal-containing compounds to hydrogen sulfide, ammonia,and metal forms capable of being deposited in the catalyst,respectively. Most usually, the catalyst is maintained as a fixed bedwith the hydrocarbon oil passing downwardly therethrough, and thereactor is generally operated under conditions selected from those shownin the following Table 1:

                  TABLE 1                                                         ______________________________________                                        Operating Conditions                                                                         Suitable Range                                                                             Preferred Range                                   ______________________________________                                        Temperature, °F.                                                                      500-900      600-850                                           Hydrogen Pressure, p.s.i.g.                                                                    100-3,000    500-2,500                                       Space Velocity, LHSV                                                                         0.05-5.0     0.1-3.0                                           Hydrogen Recycle Rate,                                                                         500-15,000  1,000-10,000                                     scf/bbl                                                                       ______________________________________                                    

The invention is further illustrated by the following examples which areillustrative of specific modes of practicing the invention and are notintended as limiting the scope of the invention as defined in theappended claims.

EXAMPLE I

A catalyst prepared in accordance with the invention is tested undertypical hydrodesulfurization conditions against two differently preparedreference catalysts consisting of particles of commercially availablecatalysts. The first commercial catalyst has a 1/20 inch trilobalcross-sectional shape and has a nominal composition of 15.0 weightpercent of molybdenum components, calculated as MoO₃, 5.0 weight percentof cobalt components, calculated at CoO, 1.0 weight percent ofphosphorous, calculated as P, and the balance of gamma alumina. Thesecond commercial catalyst has a 1/20 inch trilobal cross-sectionalshape, pore size distribution similar to the catalyst of the inventionand a nominal composition of 20.0 weight percent of molybdenumcomponents, calculated as MoO₃, 5.0 weight percent of cobalt components,calculated as CoO, 3.0 weight percent of phosphorus components,calculated at P, and the balance of gamma alumina. The catalyst of theinvention compared against the commercial catalysts is prepared asfollows:

Catalyst 1

An impregnating solution of the invention is prepared by placingammonium heptamolybdate (36.2 grams) in a beaker containing 45 ml ofwater and partially dissolving by stirring for one minute. Undissolvedammonium heptamolybdate is dissolved by stirring into the resultingsolution about 29 grams of citric acid (monohydrate). Cobalt nitrate (Co(No₃)₂.6H₂ O) in the amount of 20.4 grams is then dissolved in theresulting solution. After dissolution of the cobalt nitrate, animpregnant solution having a volume of 95 ml and a pH of about 0.29 isobtained. This solution is stable and may be stored for two weeks orlonger prior to impregnation.

Gamma alumina support particles (125 grams), having a pore sizedistribution as shown in Table II, are then contacted with theimpregnant solution. Substantially all 95 ml of the impregnant solutionis taken up by the support.

The impregnated composition is allowed to stand (age) for two hoursfollowing which it is oven dried at 110° C. and then calcined at 1,100°F. for 1/2 hour in flowing air. The final catalyst has a pore sizedistribution as shown in Table II and contains 18.0 weight percent ofmolybdenum components, calculated as MoO₃, and 3.3 weight percent ofcobalt components, calculated as CoO.

                  TABLE II                                                        ______________________________________                                        PORE SIZE DISTRIBUTIONS AND SURFACE AREAS                                                Support         Catalyst 1                                         Pore         Pore     % of     Pore   % of                                    Diameter,    Volume,  total    Volume,                                                                              total                                   Angstroms    cc/gram  p.v.     cc/gram                                                                              p.v.                                    ______________________________________                                        50-60        0.03     5        0      0                                       60-70        0.09     14       0.01   2                                       70-80        0.17     27       0.03   6                                       80-90        0.17     27       0.07   15                                       90-100      0.06     10       0.10   21                                      100- 120     0.06     9        0.18   38                                      120-150      0.01     2        0.05   10                                      150-200      0.01     1        0.01   2                                         200-10,000 0.03     5        0.03   6                                       TOTAL PORE   0.63              0.48                                           VOLUME                                                                        SURFACE AREA 250               165                                            m.sup.2 /gram                                                                 ______________________________________                                    

The catalyst of the invention and the reference catalyst are then eachpresulfided by contact with Kawait vacuum gas oil (VGO) "spiked" withdimethyl sulfide to a 2.9 weight percent sulfur content in the presenceof hydrogen flowing at 2,000 standard cubic feet per barrel (scf/b).After heating the reactor containing the catalysts to 250° F., thespiked vacuum gas oil was introduced at a liquid hourly space velocity(LHSV) of 2.5. The temperature is gradually increased hourly by 50° F.until 600° F. is reached, except the temperature is held at 400° F. forten hours and at 600° F. for two hours. The feedstock is then switchedto Light Arabian VGO, the properties of which are shown in Table III,fed at a rate of 2.5 LHSV. The temperature is increased hourly by 20° F.to a temperature of 730° F.

                  TABLE III                                                       ______________________________________                                        FEEDSTOCK PROPERTIES                                                          ______________________________________                                        Feed Description     Light Arabian VGO                                        Gravity, °API 20.8                                                     Sulfur, X-ray, Wt. % 2.54                                                     Nitrogen, Wt. %      0.090                                                    Pour Point, °F.                                                                             +95                                                      Carbon Residue on    0.42                                                     10% Botts, D-189, Wt. %                                                       ASTM D-1160 Distillation, °F.                                          IBP/5 Vol. %         623/700                                                  10/20                737/776                                                  30/40                810/837                                                  50/60                860/898                                                  70/80                928/968                                                  90/95                1,019/1,056                                              EP/Rec., Vol. %      1103/99.0                                                ______________________________________                                    

Catalyst 1 is then tested to determine its activity and temperatureincrease requirement (TIR), i.e., stability for hydrodesulfurization incomparison to the reference commercial catalyst The catalyst is chargedto a reactor and utilized at 730° F. to hydrodesulfurize a Light ArabianVGO feedstock having the characteristics shown in Table III under thefollowing conditions: 64 psig total pressure, 2.5 LHSV, and hydrogenrate of 1,500 SCF/B. The feedstock is contacted with the describedcatalysts in a single-stage, single-pass system with once-throughhydrogen such that the effluent sulfur concentration is maintained at0.15 weight percent sulfur, equivalent to about 94 percentdesulfurization.

Giving the reference commercial catalyst an arbitrary activi:y of 100,relative activities of the catalyst of the invention compared to thereference commercial catalyst are determined by calculation andtabulated in Table IV. These determinations are based on a comparison ofthe reaction rates for desulfurization obtained from the data of theexperiment according to the following standard equation which assumesone and one-half order kinetics for desulfurization: ##EQU1## whereS_(fr) and S_(pr) are the respective concentrations of sulfur in thefeed and product obtained with the reference catalyst and S_(f) andS_(p) are the respective concentrations of sulfur in the feed andproduct obtained with a catalyst being compared to the reference.

The temperature increase requirement (TIR) determinations are based uponcalculation by a relatively simple formula. TIR may be determined bydividing the difference between two operating temperatures required togive a specific product on two given days in a run by run lengthinterval between these days.

                  TABLE IV                                                        ______________________________________                                        Composition                    Stability                                      MoO.sub.3    CoO     P               TIR                                      Wt. %        Wt. %   Wt. %    Activity                                                                             °F./day                           ______________________________________                                        First   15.0     5.0     1.0    100    .58                                    Com'l. Ref.                                                                   Second  20.0     5.0     3.0    103    .33                                    Com'l. Ref.                                                                   Catalyst 1                                                                            18.0     3.3     0      121    .22                                    ______________________________________                                    

The data summarized in Table IV indicate that the temperature increaserequirement (TIR) calculated in °F./day is substantially lower for thecatalyst of the invention as compared to the reference catalysts. Thedeactivation rates of the first and second reference catalysts arerespectively more than 2.5 and 1.5 times greater than is the case withthe catalyst of the invention. In addition to this superiority instability, the catalyst of the invention also exhibits substantiallyimproved activity compared to the reference catalysts. Althoughcontaining a larger percentage of active components than the catalyst ofthe invention and still having a similar pore size distribution, thesecond commercial catalyst is not nearly as active or stable.

EXAMPLE II

Catalysts prepared in accordance with the invention are under typicalhydrodemetallization conditions against a reference catalyst consistingof particles of a commercially available demetallization catalyst. Thecommercial catalyst has a 1/20 inch trilobal cross-sectional shape andhas a nominal composition of 12.0 weight percent of molybdenumcomponents, calculated as MoO₃, 4.0 weight percent of cobalt components,calculated at CoO, and the balance of gamma alumina. The catalystscompared against this commercial catalyst are prepared as follows:

Catalyst 2

An impregnating solution of the invention is prepared by placingammonium heptamolybdate (8.5 grams) in a beaker containing 70 ml ofwater and partially dissolving by stirring for one minute. Undissolvedammonium heptamolybdate is dissolved by stirring into the resultingsolution about 6.8 grams of citric acid (monohydrate). After dissolutionof the ammonium heptamolybdate and citric acid, an impregnant solutionhaving a volume of 89 ml and a pH of about 1.2 is obtained. Thissolution is stable and may be stored for two weeks or longer prior toimpregnation.

Gamma alumina support particles (96 grams), having a pore sizedistribution as shown in Table V and yielding a pH value of 8.2 indeionized water, according to the support pH test, are then contactedwith the impregnant solution. Substantially all 89 ml of the impregnantsolution is taken up by the support.

Catalyst 3 and 4

Another impregnating solution of the invention is prepared by placingammonium heptamolybdate (17 grams) in a beaker containing 140 ml ofwater and partially dissolving by stirring into the resulting solutionabout 13.6 grams of citric acid (monohydrate). Seventeen and one-half(17.5) grams of cobalt nitrate (Co (NO₃)₂.6H₂ O) is then dissolved inthe resulting solution. After dissolution of the cobalt nitrate,ammonium heptamolybdate and citric acid, an impregnant solution having avolume of 178 ml and a pH of about 1.0 is obtained. This solution isstable and may be stored for two weeks or longer prior to impregnation.The 178 ml of impregnant solution is divided into 89 ml portions andutilized to prepare Catalysts 3 and 4.

In the preparation of Catalyst 3, gamma alumina support particles (96grams), having a pore size distribution as shown in Table V and yieldinga pH value of 8.2 in deionized water, according to the support pH test,are then contacted with the impregnant solution. Substantially all 89 mlof the impregnant solution is taken up by the support.

In the preparation of Catalyst 4, gamma alumina support particles (96grams), having a pore size distribution as shown in Table V and yieldinga pH value of 6.1 in deionized water, according to the support pH test,are then contacted with the impregnant solution. Substantially all 89 mlof the impregnant solution is taken up by the support.

The impregnated compositions of Catalysts 2, 3 and 4 are allowed tostand (age) for two hours following which they are oven dried at 110° C.and then calcined at 1,100° F. for 1/2 hour in flowing air. The finalCatalyst 1 has a pore size distribution as shown in Table V and containsabout 6.0 weight percent of molybdenum components, calculated as MoO₃,and the balance of gamma alumina. The final Catalysts 3 and 4 have apore size distribution as shown in Table V and contain about 6.0 weightpercent of molybdenum components, calculated as MoO₃, 2.0 weight percentof cobalt components, calculated as CoO, and the balance of gammaalumina.

                  TABLE V                                                         ______________________________________                                        PORE SIZE DISTRIBUTIONS AND SURFACE AREAS                                                Support     Catalysts 2, 3 and 4                                   Pore         Pore      % of    Pore    % of                                   Diameter,    Volume,   total   Volume, total                                  Angstroms    cc/gram   p.v.    cc/gram p.v.                                   ______________________________________                                         40-100      0          0      0       0                                      100-150      0.25      28      0.05    7                                      150-200      0.35      39      0.30    40                                     200-250      0.17      19      0.32    43                                     250-300      0.01       1      0.02    3                                      300-500      0.03       3      0.02    3                                        500-10,000 0.09      10      0.03    4                                      TOTAL PORE   0.90      100     0.74    100                                    VOLUME                                                                        SURFACE AREA 150               130                                            m.sup.2 /gram                                                                 ______________________________________                                    

The catalysts of the invention and the reference catalyst are then eachpresulfided for about 16 to about 20 hours by contact with a gasconsisting of 90 volume percent H₂ and 10 volume percent H₂ S flowing at4.4 SCFH at one atmosphere pressure. The temperature during thepresulfiding is initially at room temperature, is increased graduallyuntil 700° F. is reached, and then lowered to 550° F., at which time thecatalyst is contacted with the feedstock.

The Catalysts 2, 3 and 4 and the reference catalyst are then tested todetermine their hydrodemetallization activities and temperature increaserequirements (TIR), i.e., stability (or resistance to deactivation). Thepresulfided Catalysts 2, 3 and 4 and the reference catalyst are eachcharged in separate runs to a reactor and utilized at 740° F. for 8 daysand then raised to 760° F. to hydrodemetallize a Heavy Arabianatomospheric residua feedstock having the characteristics shown in TableVI below under the following conditions: 2,000 p.s.i.g. total pressure,1.0 LHSV, and a hydrogen rate of 6,000 SCF/B.

                  TABLE VI                                                        ______________________________________                                        FEEDSTOCK PROPERTIES                                                          ______________________________________                                        Feed Description   Heavy Arabian                                                                 Atmospheric Residua                                        Gravity, °API                                                                             13.0                                                       Sulfur, wt. %      4.28                                                       Nitrogen, wt. %    0.259                                                      Vanadium, ppm      97                                                         Nickel, ppm        28                                                         Ash, ppm           189                                                        Carbon Residue, D-189, wt. %                                                                     11.9                                                       Asphaltenes, (UTM-86), wt. %                                                                     14.6                                                       Pour Point, °F.                                                                           +12° C. (54° F.)                             ______________________________________                                        ASTM D-1160 Distillation                                                      Volumetric Cut     °F.                                                 ______________________________________                                        IBP                507                                                        5                  644                                                        10                 701                                                        20                 789                                                        30                 861                                                        40                 930                                                        50                 1,012                                                      60                 0                                                          Max                1,026                                                      Rec                53.0                                                       ______________________________________                                    

A portion of the feedstock is passed downwardly through each reactor andcontacted with the described catalysts in a single-stage, single-passsystem with once-through hydrogen such that the effluent metalsconcentration is maintained at 15 ppm, equivalent to about 90 percentdemetallization, for 37 days.

Giving the reference commercial catalyst an arbitrary activity of 100,relative activities of the catalysts of the invention compared to thereference commercial catalyst are determined by calculation andtabulated in Table VII. These determinations are based on a comparisionof the reaction rates for demetallization obtained from the data of theexperiment according to the following standard equation which assumesone and two-tenths order kinetics for demetallization: ##EQU2## whereM_(fr) and M_(pr) are the respective concentrations of contaminantmetals in the feed and product obtained with the reference catalyst andM_(f) and M_(p) are the respective concentrations of contaminant metalsin the feed and product obtained with a catalyst being compared to thereference.

The temperature increase requirement (TIR) determinations are based uponcalculations similar to Example I.

                  TABLE VII                                                       ______________________________________                                               Composition              Stability                                            MoO.sub.3                                                                           CoO     pH               TIR                                            Wt. % Wt. %   (support) Activity                                                                             °F./day                          ______________________________________                                        Commercial                                                                             12.0    4.0     --*     100    1.0                                   reference                                                                     Catalyst 2                                                                             6.0     0.0     8.2     147    1.0                                   Catalyst 3                                                                             6.0     2.0     8.2     144    1.0                                   Catalyst 4                                                                             6.0     2.0     6.1     120    1.0                                   ______________________________________                                         *no support pH test (catalyst prepared by comulling)                     

The data summarized in Table VII indicate that Catalysts 2, 3 and 4exhibit an improved demetallization activity compared to the commercialreference catalyst, despite containing far less active Group VIB metalcomponents and, in one instance, initially no active Group VIII metal.In addition to this superiority in activity, the catalysts of theinvention also exhibit equivalent TIR's compared to the commercialreference catalyst. Thus, catalysts of the invention may operate longerat milder conditions, (i.e., lower start of run temperatures) and haveextended life compared to the commercial reference catalyst.

Catalyst 2, differing from Catalyst 4 by the absence of cobalt metalcomponents and the support pH test, and Catalyst 3, differing fromCatalyst 4 by the pH support test, are both more active fordemetallizing the residuum oil fraction than Catalyst 4. Catalyst 4 ofthe invention is substantially more active than the commercial referencecatalyst, but Catalysts 2 and 3, containing supports with a pH supporttest value of 8.2, are for more active for demetallizing a hydrocarbonthan are either Catalyst 4 or the commercial reference catalyst.

EXAMPLE III

An impregnant solution is prepared in a similar manner as the solutionutilized to prepare Catalyst 2 in Example II except no citric acid isadded to the solution. The resulting solution has a pH of about 4.9 andis relatively unstable, not storable for more than a day prior toimpregnation of support particles.

EXAMPLE IV

Impregnant solutions 1 through 6 are prepared, five with a citric acidsolution, and each observed for pH and stability. Solutions 1 through 6contain 10 ml portions of 0.28 molar ammonium heptamolybdate (AHM)solution and 2 molar chromium nitrate solution. Prior to addition ofchromium nitrate solution to AHM in solutions 2 through 6, respectiveportions containing 2.5, 5, 6.6, 7.5 and 10 ml of 2 molar citric acidsolution are added to clear a slightly cloudy AHM solution.

Data derived from observation of pH, color and precipitation forimpregnant solutions 1 through 6 are summarized in Table VIII.

                                      TABLE VIII                                  __________________________________________________________________________    CATALYST IMPREGNANT SOLUTIONS                                                                             2 M                                               Mole Ratio         2 M      Chromium                                                                             After Two Weeks                            Sol.                                                                             Citric Acid/                                                                         0.28 M AHM                                                                             Citric Acid                                                                            Nitrate                                                                              pH                                         No.                                                                              AHM    Solution, ml                                                                         + Solution, ml                                                                         + Solution, ml                                                                         ±0.01                                                                          Ppt.                                                                              Color                              __________________________________________________________________________    1  0      10       0        10      0.41*                                                                            Yes**                                                                             Green                              2  0.5:1  10       2.5      10      0.42*                                                                            Yes**                                                                             Green                              3    1:1  10       5        10     0.43                                                                              No  Blue-Green                         4  1.3:1  10       6.6      10     0.37                                                                              No  Blue                               5  1.5:1  10       7.5      10     0.32                                                                              No  Blue                               6    2:1  10       10       10     0.31                                                                              No  Blue                               __________________________________________________________________________     *pH of solution above the precipitate                                         **precipitate upon contact of chromium nitrate with AHM                  

The data summarized in Table VIII indicate the effect upon solutionstability as a function of the mole ratios of citric acid to molybdenum(in AHM) for impregnant solutions 1 through 6. Solutions 3 through 6,having a mole ratio of at least 1 to 1, are observed to be stable for atleast 2 weeks.

While particular embodiments of the invention have been described, itwill be understood, of course, that the invention is not limited theretosince many obvious modifications can be made, and it is intended toinclude within this invention any such modifications as will fall withinthe scope of the appended claims.

We claim:
 1. A catalytic oxidation process wherein a hydrocarbon oil isoxidized by contact with a particulate catalyst under oxidationconditions, said catalyst comprises a composition prepared by the methodcomprising the steps of:(1) impregnating support particles with anaqueous impregnating solution comprising one or more dissolved Group VIBmetal components and citric acid, wherein said solution has a pH lessthan 1.0; and (2) calcining the impregnated support particles.
 2. Theprocess defined in claim 1 wherein said impregnating solution furthercomprises one or more Group VIII metal components.
 3. The processdefined in claim 1 wherein said impregnating solution further comprisesammonium ions.
 4. The process defined in claim 3 wherein said solutionhas a pH between 0 and 1.0.
 5. The process defined in claim 1 whereinsaid solution further comprises said dissolved citric acid, calculatedas a monohydrate, in a mole ratio to the dissolved Group VIB metaltrioxide of greater than about 1 to
 1. 6. The process defined in claim 1wherein said hydrocarbon oil is selected from the group consisting ofcrude petroleum oils and crude synthetic oils.
 7. The process defined inclaim 1 wherein said hydrocarbon oil is selected from the groupconsisting of lubricating oils, waxes, kerosene, solvent naphthas, fueloils, diesel fuels, jet fuels, heavy naphthas, light naphthas, cycleoils from cracking operations, coker distillates, cracked gasoline anddecant oils.
 8. The process defined in claim 1 wherein said conditionsinclude a temperature from about 500° F. to about 900° F. and hydrogenpressure from about 100 to about 3,000 p.s.i.g.
 9. The process definedin claim 1 wherein the calcined support particles obtained from step (2)have at least about 50 percent of the total pore volume in pores ofdiameter about 70 angstroms to about 130 angstroms.
 10. A catalyticoxidation process wherein a hydrocarbon oil is oxidized by contact witha particulate catalyst under oxidation conditions, said catalystcomprises an oxidation catalyst prepared by the method comprising thesteps of:(1) impregnating alumina-containing support particles with astable aqueous impregnating solution having a pH less than 1.0 andcomprising dissolved molybdenum components and citric acid, and (2)calcining the impregnated support particles.
 11. The process defined inclaim 10 wherein the activated support particles obtained from step (2)consist essentially of greater than about 3 weight percent of molybdenumcomponents, calculated as MoO₃.
 12. The process defined in claim 10wherein said impregnating solution further comprises Group VIII metalcomponents selected from the group consisting of cobalt and nickel. 13.The process defined in claim 10 wherein the activated support particlesobtained in step (2) comprise about 5 to about 50 weight percent of saidmolybdenum components, calculated as MoO₃, and from 0.5 to about 10weight percent of nickel or cobalt components, calculated as themonoxide.
 14. The process defined in claim 10 wherein said hydrocarbonoil is selected from the group consisting of lubricating oils, waxes,kerosene, solvent naphthas, fuel oils, diesel fuels, jet fuels, heavynaphthas, light naphthas, cycle oils from cracking operations, cokerdistillates, cracked gasoline and decant oils.
 15. The process definedin claim 10 wherein said conditions include a temperature from about500° F. to about 900° F. and hydrogen pressure from about 100 to about3,000 p.s.i.g.
 16. A catalytic oxidation process wherein a hydrocarbonoil is oxidized by contact with a particulate catalyst under oxidationconditions, said catalyst comprises an oxidation catalyst prepared bythe method comprising the steps of:(1) impregnating alumina-containingsupport particles with a stable aqueous impregnating solution having apH less than 1.0 and comprising dissolved ammonium heptamolybdate,nickel or cobalt nitrate and citric acid, wherein said solution containsmolybdenum components, calculated as MoO₃, in a total dissolvedconcentration greater than about 10 weight percent, and wherein saidsolution further contains said dissolved citric acid in a mole ratio tosaid molybdenum components greater than 1 to 1, and (2) calcining saidsupport particles obtained from step (1).
 17. The process defined inclaim 16 wherein the calcined support particles obtained from step (2)comprise about 17 to about 30 weight percent of molybdenum components,calculated as MoO₃, and about 1 to about 6 weight percent of cobalt ornickel components, calculated as the monoxide.
 18. The process definedin claim 16 wherein said support particles yield a pH to deionized waterof about 5 to about 9 prior to step (1).
 19. The process defined inclaim 16 wherein said mole ratio of citric acid to molybdenum componentsis greater than about 1.5 to 1.